Australian opal are classified into three major families; Black, Boulder and White Opal. The area that the stone is mined: Lightning Ridge, Queensland or South Australia is an important part of the opal identification.
At Evert Opals we try to ensure the customer knows where the stone is from ie South Australia, Lightning Ridge, or Queensland and then what type it is. These two pieces of information are usually sufficient to identify with sufficient precision the type of opal for the customer.
All of our fine jewellery is authenticated, certified and guaranteed.
Boulder Opal
Queensland Boulder opal is distinguishable by its hard ironstone backing. Most stones are from approximately 2.5 millimeters to 4.5 millimeters thick, depending on the overall size of the stone or cut so that the ironstone forms an adequate backing to the silica when size, shape and thickness of silica are considered. The surface can be flat, undulating or have a slight cabochon (not as pronounced in Black Opal). It is usually cut in a freeform shape to maximize the colour from the stone. This can be why some ironstone is left on the surface or just to avoid an un-saleable shape
Black Opal
•Black opal is generally oval, frequently calibrated with a high cabochon. It’s colour is of a dark background, green blue red or combination of these darker colours.
•Seam Black Opal- This opal, as the name suggests, is found in a seam with grey or black potch forming the bottom layer. This generally has a dark body colour.
•Knobby Black Opal- This is found in small roughly spherical knobbies. The potch is generally black and the body colour is dark. This is the most valuable form of Black opal due to its stability .
•Crystal Black Opal – This is transparent opal wit a play of colour within.
•“White” Black Opal- This opal while found at the ridge very closely resembles opal from Sth Aust.
White Opal
Light Opal is generally all one material, as opposed to Boulder or Black which tend to be two clearly definable materials fused together. It can be oval or free-form and often is of a calibrated size. It typically has a good cabochon. Light opal is mined mostly from Coober Pedy though some comes from Andamooka and Mintabie. Mintabie opal can come with a similar look to Black opal though usually has a telltale quality to the colour. Light opal is often used for doublets and triplets as it is easy to slice as it comes out of the ground in solid pieces(ie the whole rock is white opal)